1. Field of the Invention
The present invention relates to a polymer powder comprising a polymer cross-linked by metallic ions, such as a metallic salt of polyacrylic acid, or the like, and a composite material or a reinforcing material. The present invention also relates to a composite material based on the polymer cross-linked by metallic ions, and processes for producing the polymer powder and the composite material.
2. Description of the Related Art
There is a polymer, such as the metallic salt of polyacrylic acid cross-linked by metallic ions, or the like, which is cross-linked by metallic ions with a high density. This polymer is growingly expected to substitute for metals, because it exhibits a high heat resistance, isotropy and modulus of elasticity.
As set forth in Japanese Unexamined Patent Publication (KOKAI) Nos. 62-74,905, 62-74,906 and 62-259,818, the polymers cross-linked by metallic ions are produced by reacting polyacrylic acids and inorganic metallic ions in predetermined ratios in aqueous solutions including hydroxides of alkaline metals. The polymers are deposited as precipitates, and the precipitates are dried to make polymer powders.
No ordinary resin molding processes can be applied to the polymer powders comprising the polymers cross-linked by metallic ions, because they are thermally infusible. Hence, they are usually processed into molded bodies by heating, compressing and molding at a high pressure of several thousands kgf/cm.sup.2 or more.
The molded bodies made from the polymer powders cross-linked by metallic ions exhibit physical properties equivalent to metals, e.g., the heat resistance and the modulus of elasticity equivalent thereto. However, they suffer from disadvantages in that they exhibit such a low elongation, impact resistance and strength that they are hindered from the structural material applications.
In order to compensate the insufficient physical properties, it is possible to think of mixing a reinforcing material like fiber, etc., with the polymer powders. Such a reinforcing material mixing has been utilized for the general polymer materials. In the general polymer materials, even if the reinforcing materials are dispersed so unfavorably that they are localized in the general polymer materials, the composite materials made from the general polymer materials scarcely exhibit a sharply deteriorated strength. This results from the fact that the general polymer materials can be melted during the molding, and accordingly they can be impregnated into spaces between the reinforcing materials.
On the other hand, since the polymer powders cross-linked by metallic ions are thermally infusible as aforementioned, it is impossible to employ the conventional process in which the reinforcing materials are mixed with the molten polymer materials. Accordingly, it is only possible to mix the polymer powders cross-linked by metallic ions and the reinforcing materials in their solid forms. However, even if the polymer powders and the reinforcing materials are dispersed and mixed by using a ball mill, or the like, it is hard to mix them uniformly because they differ in their shapes. In addition, since the polymer powders cross-linked by metallic ions little exhibit a flowability during the molding, the localized reinforcing materials in the polymer powders are kept as they are even in the composite materials, and thereby they adversely affect the physical properties of the composite material considerably. As a result, the more the reinforcing materials are added, the lower the strength of the composite materials degrades. Thus, it is hardly expected to effect the improvements on the physical properties.